The prospect of using siRNAs as potent inhibitors to any gene of choice may provide a new therapeutic approach for many intractable diseases. However, a major impediment to successful development of siRNA-based therapies has been the general inability to deliver siRNA into cells in a stable and cell-specific manner in vivo using clinically relevant methods. GeneSegues has developed a novel delivery technology, sub-50 nanometer (s50) capsules, capable of efficient intracellular delivery of large molecule drugs to target tissues and cells. This is achieved by compressing large molecule drugs in sub-50 nm capsule shells formed entirely of protein or peptide ligands, to take advantage of receptor-mediated caveolar endocytosis for highly efficient transport across the cell membrane to intracellular compartments. In our pilot studies, we demonstrate effective delivery of nanoencapsulated siRNA against ?-galactosidase to ? -galcatosidase-(+) tumors at low dosing levels in mice. To build upon these promising early findings, our first aim in this proposed research entails assessing and optimizing siRNA nanocapsule formulations, including 1) developing and characterizing siRNA nanocapsule formulations for tumor-targeting by adapting results from successful research with conventional oligos, 2) comparing nanocapsule delivery to liposomal delivery in vitro, and 3) comparing nanocapsule delivery to naked delivery of modified-backbone siRNA in vivo using a model system. In a second aim focusing on therapeutic efficacy, we propose to compare nanocapsule delivery vs. naked delivery of modified-backbone siRNA against Casein Kinase 2, a recently validated cancer target, using an orthotopic xenograft model of human prostate cancer in nude mice. If successful, we expect that completion of this body of work would provide a solid framework for partnering with NIH and/or drug developers to progress encapsulated siRNA therapies forward. Manipulation of disease pathology at the gene level can lead to a cure, not just symptomatic treatment. Consequently, quality of life and survival of patients diagnosed with advanced disease would be expected to improve significantly with targeted siRNA therapeutics. The critical path to bringing siRNA therapeutics to market is effective drug delivery; potentially, this research will drive significant progress along that path. [unreadable] [unreadable]